Method for thermoforming a screw cap closure

ABSTRACT

A method for thermoforming a screw cap closure wherein a flat sheet or web of thermoplastic material is initially heated and placed over a female mold cavity and a male mold is pressed against the heated plastic sheet to draw a portion of the sheet into the female mold cavity. Air is injected into the mold at two points; the first being through the top of the male mold thereby to expand the plastic sheet against the lower portion of the female mold and the second is through the upper portion of the female mold to force the sheet to conform tightly against thread forming contours which are provided on the male mold. The male mold is then withdrawn bringing the formed cap in the web with it and the mold is twisted out of the formed cap, leaving the formed cap in the web.

March 21, 1912 G, MENKEL 3,651,185

METHOD FOR THERMOFORMING A SCREW CAP CLOSURE Filed Dec. 17, 1969 4Sheets-Sheet 1 FIG.|

INVENTOR GARY G. MENKEL BY M, M M-IJL ATTORNEYS March 21, 1972 MENKEL3,651,185

METHOD FOR 'IHERMOFORMING A SCREW CAP CLOSURE Filed Dec. 17, 1969 4Sheets-Sheet 2 FIG. 2

INVENTOR GARY G. MENKEL Q4 7 5 mwi%"- ATTORNEYS March 21, 1972 MENKEL3,651,185

METHOD FOR THERMOFORMING A scxmw CAP CLOSURE Filed Dec. 17, 1969 4Sheets-Sheet 5 INVENTOR GARY G. MENKEL BY ATTORNEYS 4 Sheets-Sheet 4.

G. G. MENKEL METHOD FOR THERMOFORMING A SCREW CAP CLOSURE March 21, 1972Filed Dec.

INVENTOR GARY G. MENKEL [2 z I 972 r 6 5 5 ATTORNEYS FIG.5

3,651,185 METHOD FOR THERMOFORMING A SCREW CAP CLOSURE Gary G. Menkel,Holliswood, N.Y., assignor to Design Center, Inc., Long Island City,N.Y. Filed Dec. 17, 1969, Ser. No. 885,848 Int. Cl. B29c 17/04 US. Cl.264-89 6 Claims ABSTRACT OF THE DISCLOSURE A method for thermoforming ascrew cap closure wherein a fiat sheet or web of thermoplastic materialis initially heated and placed over a female mold cavity and a matingmale mold is pressed against the heated plastic sheet -to draw a portionof the sheet into the female mold cavity. Air is injected into the moldat two points; the first being through the top of the male mold therebyto expand the plastic sheet against the lower portion of the female moldand the second is through the upper portion of the female :inold toforce the sheet to conform tightly against thread forming contours whichare provided onthe male mold. Themale mold is then withdrawn bringingthe formed cap in the web with it and the mold is twisted out of theformed cap, leaving the formed cap in the web.

This invention pertains to'a method for thermoforming a. screw capclosure and more in particular to a method and apparatus to thermoform ascrew cap closure using both a male and female mold and the introductionof an auxiliary molding force at two separate locations within the moldcavity.

Thermoformed screw cap closures, for example to seal plastic containersor jugs, are finding an ever increasing demand. Heretofore, such screwcap closures have been formed by a variety of processes utilizing aheated sheet of a thermoplastic material which is then placed in afemale mold and placed under a vacuum to draw the heated sheet ofplastic material into the mold or by using a male'mold and drawing theheated sheet of thermoplastic material over'the mold to form the desiredscrew cap closure shape. In addition, male mold forms have been used topunch the desired screw cap closure shape out of a heated sheet ofthermoplastic material. While these methods have proven to be somewhatsatisfactory in forming thermoformed screw cap closures, they have notresulted in the production of a thermoformed screw cap closure havingclose tolerances in the critical dimensions of the screw cap form and ofthe lid of the screw cap closure to provide a tight and effective sealbetween the screw cap closure and the opened mouth of the jug or bottlewith which it is used.

Accordingly, it is an object of the present invention to provide amethod for producing thermoformed screw cap closures within closelycontrolled tolerance ranges in order to provide an effective sealingclosure for plastic bottles or jugs.

It is a further object of the present invention to provide a method forproducing thermoformed screw cap closures of a high quality in a highlydependable and efiicient manner.

A still further object of the present invention is to provide a methodfor producing thermoformed screw cap closures utilizing both a male anda female mold and the introduction of positive air pressure at twolocations within the molds in order to closely control the criticaldimensions of the screw cap closure.

These and other objects and advantages of the present United StatesPatent invention will become more readily apparent with the 3,651,185Patented Mar. 21, 1972 "ice consideration of the following specificationin conjunction with the accompanying drawings.

In the drawings:

FIG. 1 is an elevational view, partly in section, showing one set ofmale and female molds positioned with respect to a heated sheet ofthermoplastic material prior to the forming operation;

FIG. 2 is a view similar to FIG. 1 showing the position of the male andfemale molds and the thermoplastic sheet after the two molds have beenbrought together and air has been forced against the heated plasticsheet within the mold cavity;

FIG. 3 is a view similar to FIG. 2 showing an alternate embodiment;

FIG. 4 is an elevational view showing a portion of the male and femalemold assembly including the rotative means to rotate the formed screwcap closures off the male mold; and

FIG. 5 is a perspective view of the completed screw cap closure formedby the method and apparatus of the present invention.

With reference now to FIG. 1, there is shown a sheet or web 10 of heatedthermoplastic material which is placed between a female mold cavity 12and a male mold form 14 prior to insertion of the male mold form 14 intothe female cavity 12 to thermoform a screw cap closure. The female mold12 is constructed from a number of separate elements for convenience inassembly; however, it is to be understood that the mold could be formedout of a solid piece of material if so desired.

Mold 12 includes a first side wall forming portion 13 having acylindrical opening 16 therein with an undercut shoulder portion 18which communicates with an air supply passage 20 through portion 13connected to a source of air under pressure (not shown). Immediatelyadjacent the wall forming portion 13 in the female mold 12 is a ringmember 22, which may be formed from any rigid metallic or plasticmaterial having a rounded nodular portion 24 extending into thecylindrical opening of the female cavity 12. Brass has been found to bea desirable material for ring member 22 because it is relatively easy tomachine and polish to a smooth finish. Adjacent the ring member 22 is asecond wall forming member 26 which also has a cylindrical opening 28therein having a slightly smaller diameter than the cylindrical opening16 in wall forming portion 13. The internal wall surface of cylindricalopening in wall forming portion 26 includes a plurality of spacedindentations 30 provided around the periphery of the opening 28 for apurpose to be explained more fully hereinbelow.

The die cavity 12 is closed at its lower end by a block 32 having acylindrical opening 34 therein through which is inserted a cylindricalplug member 36. Plug member 36 has a tapered end segment 38 and the plug36 extends into the die cavity of female mold 12 beyond the edge portion40 of the block 32 so that the lower portion of the mold 12 has a flatsurface configuration formed by edge 40 of block 32 and a raisedportionformed by the taper 38 of plug member 36 and another flat surfaceconfiguration formed by the flat top 42 of plug member 36. This portionof mold 12 defines the top of the cap closure configuration as will beexplained more fully hereinbelow.

The male mold portion 14 comprises a substantially cylindrical portion44 having protrusions 46 thereon in the general contour of, and spacedto form, a screw thread configuration. The male mold 14 is again made intwo pieces, a dome-shaped lower portion 48 and the screw formcylindrical portion 50 having a cylindrical support shaft 52 connectedthereto.

The cylindrical portion 50 also includes, adjacent the end which isjoined to dome-shaped portion 48,'a cylin- 'drica-l 'cavityflwhichcommunicates with an'axially dis -'48-.includes a plurality of airpassages 58 through the lower surface of dome-shaped-portion 48. Thus,when portion 48 and cylindrical portion 50 are assembled, as

'show1i in FIGS. 1 and .'2, air communication means are providedthroughxaxial bore 56, cavity 54 and passages 'i58.fron'1 the source: ofair 'under pressure to the exterior of the male mold 14.

:With reference 'nowto FIG. 2 as well, the thermorformed-screw cap:closure is formed by placing a flat -sheetof heated thermoplasticmaterial betweenthe male mold 14 and the-female mold cavity 12 and thenmoving the male mold portion 14 into the female mold :eavity 12 thusdrawing a portion of the thermoplast c sheet material 10 into thecavity. As best seen in FIG.

'2," once themale mold 14 has forced the thermoplastic sheet materialinto the female mold cavity 12, air under pressure is allowed to flowthrough air supply passages and 56 in order to cause the heated plasticsheet material to conform to the configuration of the respective .maleand female molds. The greatest diameter of the male mold 14, for exampleat the maximum crest height of. a screw form 46 and at the juncture 60of the portions '48 and 50, is dimensioned to provide a clearancebetween the male mold form 14 and the wall of the female cavity 12 inexcess of the thickness of the thermoplastic sheet 10'. Hence, absentthe pressure of an auxiliary molding force, such as air pressure, therewould be insufiicient cooperation between the mating of the two molds toform a precisely dimensioned screw cap closure.

As seen most clearly in FIG. 2, the ring member 22 with its nodularportion 24 extends radially inwardly within the female mold cavity 12and is dimensioned so as to contact the sheet of thermoplastic material10 and pinch the thermoplastic material between the male mold 14, forexample in the area adjacent the juncture 60, and the nodular portion24. This provides an efl ective air seal between the upper and lowerportion of the female mold and serves to isolate the upper and lowerportion of the mold. Hence, when air pressure is simultaneouslyintroduced through air passages 20 and 56, there is an effective airseal between the upper and lower portions of the mold to segregate theair flow from air .passage 20 and the air flow from air passage 56,respectively, to the upper and lower portions'of the mold. Thus, the airflowing through air passage 20 flows circumferentially around the femalemold cavity 12 within undercut shoulder portion 18 and forces the heatedthermoplastic material against the thread forming contours on the malemold member 14. Simultaneously, the air flowing through air passage 56passes through air holes 58 and causes the thermoplastic sheet materialin the lower portion of the mold to expand away from the domeshapedportion 48 of male mold 14. This segment of thermoplastic sheetmaterial10 expands away from the portion 48 of male mold 14 and conforms to theconfigz uration .of the lower portion of female mold 12. As thethermoplastic sheet material expands outwardly against the confinementof the female mold, discrete portions of the-thermoplastic sheetmaterial are forced into the spaced indentations around the periphery ofmold portion 28 ,to form circumferentially spaced protrusions in theformed screw cap closure. I

While the method of the present invention has been describedasutiliz'ingpositive :air pressure through air passages 20 and 56, it isto be understood that vacuum plies-sure or; a combination of positiveand vacuum pressute .could also be used. With reference to FIG. 3, themale mold.14 is shown having the air passage 56 and cavity as in-theembodiment'of FIGJZbut the plurality of air passages 58' radiateradially outwardly from cylindricalcavity 54. Thus, when a vacuum isapplied across air 'pas'sa'ge -'56,tlie 'th'ermoplasticmaterial 10 willbe if so'desired. I

With reference now, to FIG.,4,,,once the screw cap closure has beenformed by movingthemale mold with a thermoplastic sheet of 'heated'material' into-the female mold cavity and the thermoplasticmaterialleftto; set and cool, the male mold is retractedwith respect to thefemale mold cavity drawing the formedscrew cap clo sure in the web 10withit simultaneously, the malemold is rotated about its central axistoallow the male mold to disengage from the screwicapclosure. As seen-in IFIG.

v3, a plurality of female molds 12 are positioned in a stationarymounting block 70 and a plurality of male molds 14 are rotatably mountedwithin a moving mounting block 72 which is adapted to move verticallywith respect to stationary block 70 to allow the male moldto move intothe female mold cavity 12. Supporting shaft 52 for each male mold isrotatably journaled within the moving block 72 and is provided withappropriate sealingmeans such as O-ring seals 74 within a groove 76cut., in t o the circumference of shaft 52.. As explained above, themale mold 14 is secured to one end of shaft 52 and, at the other end,shaft 52 is provided with a gear 76 fixed thereto. Block 72 is alsoprovided with a rack 78 having teeth 80 thereon which engage'and'meshwith the teeth-on gear 76 and rack 78 is adapted to be movedtransversely'of gears 76 thereby to cause rotation of the gears.Rotation of the gears thus causes rotation of shaft 52 and male mold 14secured thereon. Hence, when'moving block 72 is retracted with respectto fixed block' 70, rack 78 is moved with respect to moving block 72 tosimultaneously cause rotation of male member 14i to allow the-male moldto unscrew from the formed screw cap closure. After the screw capclosures have been formed in th'e web 10 and the moldshave beenseparated, the web is transferred out from betweenthe'male andfemalelmolds and the formed screw cap closures-are 'separated'from web10 by a trimming operation. 5 f-, 1 1

Reference is now made to 5 which shows-a screw cap closure completedaccording to the method and apparatus of the present invention. Thescrew cap ;closurel80 has a substantially planar top portion 82anda'-;depending skirt portion 84 withthedepending skirt portion 84 beingprovided with a screw formed configuration formed by the screwformconfiguration 46 on themale mold 14. Around the vperiphery ofthejuncture between the substantially planar top 82-and depending skint-v84are provided a plurality of protrusions 86 which were formed by thatportion ofthe, thermoplastic material which flowed into protrusions 30'in-ithe female. mold cavity. The planar top 82 is also formedwithacircumferential annular groove 88 sothat a" peripheral portion 90 ofthe top is at a slightly higher elevation than the central portion 92due to adherence of the top during formation to the cylindrical plugmember 36 in the female die cavity 12. Reference is made to applicantscopending application filed on even date herewith (andideiitified by CMSFile No. 24766), which application is incorporated herein by reference,for a more detailed and fuller explanation of the construction, featuresand advantages of the screw cap closure 80 formed by the method andapparatus of the present invention.

It is thus seen that by the method "and apparatus. of the presentinvention a thermofonned screw cap' closure is formed which has superiorsealing properties" dueto the precise control of the critical dimensionsof the cap during the thermoforming process.

What is claimed is: 1. A method for thermoforming a screw cap closurecomprising:

heating a sheet of thermoplastic material; placing said heated sheet ofthermoplastic material between separated male and female mold forms;

moving at least one of said male and female mold forms relative to theother to telescopically engage said mold forms thereby drawing a portionof said heated thermoplastic material into said female mold form;

said male and female mold forms being provided with air passage meanscommunicating with a source of pressurized air;

providing air under pressure to selected portions of each of said maleand female mold forms to cause said heated thermoplastic material toconform to the configuration of the male and female mold forms in orderto closely control the dimensions of said thermoformed screw capclosure; and

sealing said heated thermoplastic material while said mold forms aretelescopically engaged to provide an air seal between the air passagemeans in said male mold form and air passage means in said female moldform thereby to form at least two separate chambers within saidtelescoped mold forms.

2. The method as defined in claim 1 including providing said male moldform with screw thread forming protrusions thereon and wherein said airpassage means in said female mold form is located adjacent the screwthread forming protrusions on said male mold form whereby when air isintroduced through said air passage means in said female mold form saidthermoplastic material is forced to closely conform to the screw threadforming protrusions on said male mold form.

3. The method as defined in claim 1 including the step of moving atleast one of said male and female mold forms out of telescopicengagement after said screw cap closure has been formed andsimultaneously rotating said male mold form about its longitudinal axisto free a said completed screw cap closure from engagement with saidmale mold form.

4. A method for thermoforming a screw cap closure comprisingfi I heatinga sheet of thermoplastic material; placing said heated sheet ofthermoplastic material 'between separated male and female mold forms;moving at least one of said male and female mold forms relative to theother to telescopically engage said mold forms thereby drawing a portionof said heated thermoplastic material into said female mold form; saidmale and female mold forms being provided with air passage meanscommunicating with means to impress a vacuum across said air passagemeans;

providing a vacuum across selected portions of said male and female moldforms to cause said heated thermoplastic material to conform to theconfiguration of the male and female mold forms in order to closelycontrol the dimensions of said thermoformed screw cap closure; and

sealing said heated thermoplastic material while said mold forms aretelescopically engaged to provide an l air seal between the air passagemeans in said male mold form and air passage means in said female moldform thereby to form at least two separate chambers within saidtelescoped mold forms.

5. The method as defined in claim 4 including providing said male moldform with screw thread forming protrusions thereon and wherein said airpassage means in said male mold form are located adjacent the screwthread forming protrusions on said male mold form whereby when a vacuumis impressed across said air passage in said male mold form saidthermoplastic material is forced to closely conform to the screw threadfor-ming protrusions on said male mold form.

6. The method as defined in claim 4 including the step of moving atleast one of said male and female mold forms out of telescopicengagement after said screw cap closure 'has been formed andsimultaneously rotating said male mold fonm about its longitudinal axisto free said completed screw cap closure from engagement with said malemold form.

References Cited UNITED STATES PATENTS 3,337,664 8/1967 Lyon 264-893,338,997 8/1967 Tigner 264-296 X 3,444,282 5/1969 Burkett 264-92 X2,799,049 7/ 1957 Wilson 1'8-2 RS X 3,102,304 9/1963 Divers 18-2 RS X3,290,418 12/ 1966 Best 264-92 3,507,942 4/1970 Lynch 264-94 X ROBERT F.WHITE, Primary Examiner I. H. SILBAUGH, Assistant Examiner US. Cl. X.R.

18-2 RS, 5 BV, 19F; 249-59; 264-92, 94, 334

